The present invention relates to semiconductor fabrication, and more particularly, to pulse plasma matching systems and methods.
In general, the electrical impedance inside a plasma chamber in a semiconductor manufacturing apparatus can be affected by the materials used in the interior of the chamber. In particular, variations in the materials may greatly influence the plasma chamber to which a radio frequency (RF) power source is applied. For example, in a sputtering process using AZO (Al-doped ZnO) as a deposition material, when the AZO corrodes, the impedance of the chamber interior can change. As a result, a process, such as an etching or ashing process, may be changed depending on process conditions, such as the size of processed substrate, the process gases used and/or temperature, etc., of the chamber interior. The most desirable RF matching condition in a plasma chamber system is typically to make an internal impedance of the RF power source about equal to an internal impedance of the chamber. An electricity utilization level can increase by using an RF matching box in order to obtain an impedance matching between the RF power source and an electrode of the chamber.
A plasma process uses RF power. It can therefore be desirable to suppress reflective power. To reduce reflective power, a matching system including a variable capacitor and a coil can be used between an RF generator and a load, such as a plasma chamber. Most matching systems include a variable vacuum capacitor and a fixed coil, and realize power matching by using an algorithm that substantially reduces reflective power through the variable vacuum capacitor. A typical matching method uses an algorithm that searches for a point where reflective power is substantially reduced by controlling the capacitance of the variable vacuum capacitor when the reflective power is more than a reference level.
A power pulse operation method can enlarge a process area and/or increase process margins compared to continuous wave methods. The power pulse operation can obtain a high selection rate as compared with continuous wave methods, and also can solve or improve problems, such as charging damage, UV radiation, and/or physical sputtering that can be caused in plasma processes. Thus, the use of the power pulse operation has increased.
A conventional semiconductor manufacturing apparatus for matching impedance using a matching box is shown in FIG. 1.
Referring to FIG. 1, a chamber 30 ionizes gas using applied RF power that is matched through an RF matching box 60, and generates a plasma for use in performing a semiconductor manufacturing process. A power detector 40 detects a level of RF power supplied to the chamber 30 and applies it to a tuning controller 50. The tuning controller 50 monitors RF power consumed inside the chamber 30 in response to a feedback signal from the power detector 40, and processes a monitoring value according to a predetermined algorithm to maintain the RF power at a constant level, and also controls an impedance match between an RF power source 20 and the chamber 30. The RF power source 20 receives a control signal from the tuning controller 50 and generates RF power in response to the control signal. The RF matching box 60 matches impedance between the RF power source 20 and the chamber 30.
A configuration of the RF matching box 60 to match impedance between the RF power source 20 and the chamber 30 is shown in FIG. 2.
With reference to FIG. 2, the RF matching box 60 includes a power supplier 61 that supplies power to first and second motors M1 and M2. A controller 63 is coupled to the first and second motors M1 and M2. Rotational power from the first and second motors is transmitted through a plurality of gears 62 to a first variable capacitor C1, and a second variable capacitor C2. A peak voltage detector 64 is coupled to the second variable capacitor C2 through an inductor L1. A resistor R1 is also coupled to the inductor L1. RF power is output by the matching box 60 from the peak voltage detector 64. A DC voltage on the resistor R1 is supplied to the controller 63.
The power supplier 61 receives AC input power and responsively outputs a direct current voltage of 24V. The first and second motors M1 and M2 receive direct current (DC) voltage from the power supplier 61, and rotate clockwise or counterclockwise in response to a motor drive control signal from the controller 63. The controller 63 controls the first and second motors M1 and M2 in response to a peak voltage detected by the peak voltage detector 64. The plurality of gears 62 transfer rotary power from the motors M1, M2 to the first variable capacitor C1 and the second variable capacitor C2. The first variable capacitor C1 is exposed to air and is used for a coarse control. The first variable capacitor C1 includes a control knob that rotates in response to power transferred through the plurality of respective gears 62. The second variable capacitor C2 is exposed in a vacuum state, and performs a fine control. The second variable capacitor C2 includes a control knob that rotates in response to power transferred through the plurality of respective gears 62. The inductor L1 reduces/eliminates a direct current component of RF power output from the second variable capacitor C2. The resistor R1 is coupled to the inductor L1, and is used to detect a direct current bias voltage. The peak voltage detector 64 detects a peak voltage of RF power matched for impedance through the inductor L1.
In a continuous wave plasma shown in FIG. 3 using an RF power matching system as described above, a stabilized power match is possible, because there may not be a significant time delay in the feedback loop and/or the plasma may not change greatly during the feedback loop from time t1 to time t4, as shown in FIG. 4A. As shown in FIG. 4A, feedback is provided to the RF source 20 beginning at time t1. The adjusted power output from the RF power source 20 is provided to the matching box 60 beginning at time t2. The matched RF power is provided to the plasma chamber 30 beginning at time t3. At time t4, the state of the plasma in the chamber 30 changes in response to the adjusted power level.
However, in a pulse plasma system there may be a time delay in the feedback loop during which the state of the plasma can change, as shown in FIG. 4B. Thus, reflective power can be generated in a pulse plasma system, which may be an important factor limiting the use of pulse plasma system/methods. In applying a pulse plasma, it can be difficult to perform power matching because, while a feedback value is given from the chamber 30 to the RF power source 20 at a time point t1, RF power is provided from the RF power source 20 to the RF matching box 60 at a time point t2, and an RF power pulse matched for an impedance is given from the matching box 60 to the chamber 30 at a time point t3. Thus, a time delay of t4-t1 may be present in the feedback loop, as illustrated in FIG. 4B.
In a continuous wave plasma, a level of state change of the plasma during the feedback loop may not be great, so that a feedback value received from the matching box 60 can be effective even when a time delay is generated at t1 to t4 as shown in FIG. 4A. However, in a pulse plasma, a level of state change of the plasma from t1 to t4 can be large. Thus, a phase of RF power value given from the matching box 60 to the chamber 30 can be distorted due to time delay in the feedback loop, which can generate reflective power that can cause process errors.